Figure 1:Inclined bedding surface (c. 70°) displaced by a segmented strike-slip fault with 3 relays. The faulted bed geometry is identical to that at a relay zone on a normal fault offsetting horizontal beds. Sketch showsperson for scale. Outcrop located at Jaca, Pyrenees, Spain. From Walsh et al.(in review).

Figure 2:(a) Fault polygons on a map of horizon H (arrowed in (b)) with location of cross-section in (b) indicated. (b) Seismic section with interpretation of traces of a master fault and a splay intersecting at a branch-point. Vertical and horizontal scales approximately equal (1ms = c.1.25m). (c) Block diagram of fault interpretation with surface of master fault shaded, and boundaries of the splay fault defined by an L-shaped branch-line (heavy line) and curved tip-line. The plane of cross-section in (b) is indicated together with traces of master fault and splay on this section. The branch-line and tip-line of the splay fault are each defined by 10 data points on 10 seismic sections spaced at 12.5m. Note the significant proportion of the fault displacement accommodated by a continuous strain, with bed rotation, between the overlapping faults. The structure is interpreted as breaching of a normal fault relay by the footwall fault, with the relay originally terminating downwards at a branch-point at the approximate position of the cross-section. The initial breaching probably occurred at some point on the down-dip segment of the branch-line. From Walsh et al. (in press).

Figure 3:(a) Fault polygons on horizon H (arrowed in (c)) with ticks on downthrown sides, enclosing a hostrock lens. Axes of the fault bends are parallel to the normal fault slip direction. (b) U-shaped branch-line (heavy line) bounding the lens in (a), or incomplete horse, which terminates upwards at the sea floor (c). The location of the seismic section (c) is indicated. The branch-line is defined by data points (branch-points) on 42 seismic sections spaced at 25m. (c) Seismic section (as located in (a) and (b)) showing interpreted fault traces and branch-point. Note the bed rotation within the relay, accommodating a proportion of the aggregate throw across the structure. Horizontal and vertical scales are approximately equal (1ms = c.1.25m). (d) Interpreted growth sequence on horizon H for the breached relay, based on throw backstripping (Childs et al., 1993). (i) Initial relay structure, (ii) breaching by both footwall and hangingwall faults, (iii) further growth by slip mainly or exclusively on the hangingwall fault with the re-joining splay inactive. Seismic from the Timor Sea. From Walsh et al., (in press).

Figure 4:(a) Cross-section showing two large normal syn-sedimentary faults (bold) from the Northern North Sea. There are seven interpreted horizons of which 1-3 are pre-faulting, 4-6 are syn-faulting and 7 is post-faulting. The present day structure of these faults is indicated in (b) to (e). These data are derived from a seismic survey shot perpendicular to the fault strike and spaced every 100m. The faults shown in (a) link laterally along a vertical branch-line shown on the map of Horizon 1 (b). (c) Throw contoured strike projection of the two faults shown in (a); contours are in ms and the dashed line indicates the level of Horizon 4 on each fault. The throw contours on the faults are constrained by a total of c. 300 data points. (d) Horizon separation diagram of the cutoffs of Horizon 1 against the two faults. (e) Aggregate throw strike-projection of the two contour patterns in (c). (f) to (i) are the backstripped equivalents of (b) to (e) and illustrate the structure of these faults at the time when Horizon 4 was at the free surface. From Childs et al. (1995).

Contact: John Walsh
Tel: 353 1 706 2606
Email: fault@fag.ucd.ie